A myriad of optical devices or optical systems are known to process and/or analyze image information representing radiation.
Devices and methods to analyze a combustion process in a combustion chamber in order to use the data obtained by said analysis to control the combustion process are known from prior art. Combustion may be any kind of combustion such as it is used in gas turbines, in waste incinerator plants or any other machines or plants. With such devices and methods it is possible to control the supply of fuel to be added to the combustion chamber in a manner that the combustion process reaches a high rate of efficiency. Hence such devices are used to optimize the efficiency factor of the combustion process.
It is a well known technique to use specific properties of reaction products of a combustion process for flame analysis and monitoring. Such combustion radicals and gases radiate and absorb light in a certain spectral range. As an example: for C2 the wavelengths are in a range between 445 nm and 455 nm and for CH the wavelengths are between 420 nm and 440 nm.
GB 2 390 675 discloses an apparatus having an optical probe in the form of a lens for transmitting full image radiation into an imaging device. Such an imaging device may be a monochromatic CCD camera, a frame grabber and a computer. The parameters of the flame are then presented on the computer screen in a graphical or numerical manner in order to be visible for the user.
DE 197 10 206 discloses a further device for combustion analysis as well as for surveillance in a combustion chamber. Several beam splitters are used behind the lens system for full image capture in order to filter a certain spectral region of the radiation, which is of particular interest. The spectral region is then transmitted to a CCD sensor in order to be processed by a computer unit.
The use of a CCD sensor is a drawback of prior art devices, since the sampling rate of said CCD sensor is rather low. Such a low sampling rate has a negative influence on controlling the combustion process in terms of efficiency. Short time scale variation cannot be monitored reliably.
Since the combustion process in a combustion chamber of a gas turbine is carried out at very high temperatures, i.e. normally around 1200° C. to 1500° C., direct measurements inside the combustion chamber are not possible. A window between the combustion chamber and the device reduces said temperature significantly. Nevertheless the temperature on the window surface is still around 100° C. to 150° C. Due to said temperatures the use of optical elements such as objectives or beam splitters is a not a useful option.
In order to cope with high temperatures, the use of cooling systems has been proposed, e.g. in GB 2 390 675. However the use of a cooling system is rather costly in terms of installation and maintenance.
Another drawback are the optical losses of the optical systems used in devices of prior art. Furthermore it is a difficulty with devices of prior art to adjust the optical systems during maintenance or installation of the device. This usually requires professional personnel.